This application is based upon and claims priority from prior European Patent Application No. 97-830462.4, filed Sep. 23, 1997, the entire disclosure of which is herein incorporated by reference.
1. Field of the Invention
This invention relates to a MOS transistors substitutive circuit having a transformer/data interface function, particularly for ISDN networks, and corresponding control and driving switch configuration.
The invention particularly, but not exclusively, concerns an ISDN network termination, and the description that follows will make reference to that application for simplicity of illustration.
2. Description of the Related Art
As is well known, technological advancements in the telephone field have made it necessary to provide telephone terminal units with additional functions.
An important additional function is, besides voice transmission, the transmission of information relating to new products and/or services, such as facsimile operations, video communications, network interconnections, etc.
The transmission of data by a telephone terminal unit may utilize special networks. One example of a well known and widely utilized network is the ISDN (Integrated Services Digital Network), originating by natural evolution from the traditional telephone network and employing the same standard cables. This compatibility of transmission with the traditional telephone network allows the ISDN network to use the so-called telephone loops, which are advantageously available throughout the territory.
In addition, the ISDN network has a European standard, having a transmit rate of 64 kbit/sec; the ISDN network allows two talk channels plus a control and service channel to be sent over the same line, which channels can be either used by two telephone sets, or one telephone set and a facsimile, or one telephone set and a PC (Personal Computer).
Shown by way of example in FIG. 1 is a block diagram for basic access to the ISDN network. This diagram is also shown in FIG. 2, in greater detail.
The following main blocks can be distinguished in these figures:
LTxe2x80x94line termination;
NTxe2x80x94network termination;
TExe2x80x94terminal apparatus;
TAxe2x80x94terminal adapter.
Also shown in FIG. 1 are first U, second S and third R reference points, whereat special interface circuits are connected, as detailed in FIG. 2 for the references U and S only.
In particular, the line termination LT provides for power supply in the remote mode to the network termination NT, and in an emergency condition known in the art as RM (Restricted Mode), for a terminal apparatus TE as well.
Furthermore, the line termination LT allows signal data DS to be transmitted and received in suitable formats, such as the 2B1Q or 4B3T formats, through the interface circuits of the reference point U.
The terminal adapter TA, connected in the reference point R, allows apparatus designed for different data transmission modes, usually commercially available apparatus, to be also connected to the network termination NT.
The network termination NT is connected to the line termination LT by a tow-wire telephone loop, whereby the network termination NT can be powered from the line termination LT and can exchange with it data DS simultaneously in either direction.
The network termination NT is provided with a DC/DC converter CONV1 capable of delivering a supply voltage VDD, typically of 5V, to the interface circuits at the reference points U and S, as well as an emergency voltage Vem.
The emergency voltage Vem, of about 40V, can only be used in an RM emergency condition to power the terminal apparatus TE, with some suitable constraints. Such terminal apparatus TE are normally powered from an AC/DC converter CONV2 provided at the network termination NT and capable of powering up to eight terminal apparatus TE, according to the standard applied. Under normal operation conditions, the emergency voltage Vem is disconnected by means of a first switch arrangement SW, shown in FIG. 2, which is closed at the AC/DC converter CONV2.
As shown in detail in FIG. 2, the network termination NT has two input terminals A, B and four output terminals Axe2x80x2, Axe2x80x3 and Bxe2x80x2, Bxe2x80x3, two for each transformer of the interface circuit at the reference point S, as previously shown schematically in FIG. 1. The output terminals Axe2x80x2, Axe2x80x3 and Bxe2x80x2, Bxe2x80x3 provide for remote power supply and data transmission through a supply/data transmission block BT comprising a DC/DC converter CONV3, a transmit block TXxe2x80x2, and a receive block RXxe2x80x2, so as to communicate with the terminal apparatus TE. The transmit and receive blocks, TXxe2x80x2, RXxe2x80x2 are schematically represented in FIG. 2 by simple transformers serving to receive the power supply and allow conversion of the data present in the transmit and receive blocks TXxe2x80x2, RXxe2x80x2.
In particular, it should be noted that power to the terminal apparatus TE is supplied from the interface circuits at the reference point S by means of the transformers, shown schematically in FIG. 2, which are also utilized for exchanging the signal data DS. These transformers allow a virtually zero DC voltage drop to be obtained, and have an AC impedance which is a function of load and the winding ratio of the transformer. In addition, the supply to the terminal apparatus TE under RM emergency conditions is controlled through the switches SW.
The combination of the transformers in the interface circuits at the reference point S and the switches SW controlling the supply to the terminal apparatus TE form a transformer/data interface/switch circuit for effecting a polarity reversal CT.
The use of transformers, for powering or effecting the exchange of signal data DS at the interface circuits, is specially convenient from the standpoint of energy dissipation. Minimizing energy dissipation is highly important under RM emergency conditions; in such circumstances, in fact, no mains supply would be available, and the available power would be limited to the small power that the DC/DC converter at the interface circuits of the reference point U can draw on the line.
Examples of circuits which employ such transformers are described in European Patents No. 0 160 411 to Northern Telecom Limited and No. 0 639 021 and No. 0 590 242 to DeTeWexe2x80x94Deutsche Telephonwerke Aktiengesellschaft and Co.
However, these transformers must be designed to meet specific applicational requirements, thereby producing a manufacturing cost.
Also known is to use circuits including active components to provide equivalent coils in place of the transformers. Examples of such circuits are described in U.S. Pat. No. 3,649,769 to Pest, U.S. Pat. No. 4,004,104 to Picandet et al., U.S. Pat. No. 3,943,432 to Colardelle et al., and U.S. Pat. No. 4,088,843 to Rogers et al.
The prior art active component circuits are less expensive than transformers. But they are unsatisfactory from the energy dissipation standpoint, and still require suitable switches for supply control.
The underlying technical problem of this invention is to provide a transformer/data interface circuit emulating a transformer for an ISDN telephone line, which can transmit the data presented on the line, transmit and control the power supply to the terminal apparatus (reversal of current polarity or direction), and has suitable structural and functional features to afford reduced energy consumption and overcome the drawbacks that are still besetting the prior art devices.
Briefly, according to one aspect of the invention, a MOS transistors substitutive circuit having a transformer/data interface function, in particular for ISDN networks, comprises a voltage reference terminal, a supply voltage reference terminal, a ground potential reference terminal, a first data interface, and a second data interface. The circuit also comprises a first power supply/transmitter block and a second power supply/transmitter block. The first power supply/transmitter block is connected between the voltage reference terminal and the first data interface, and is further connected to the supply voltage reference terminal. The second power supply/transmitter block is connected between the ground potential reference terminal and the second data interface, and is further connected to the supply voltage reference terminal. The circuit also comprises a first MOS transistor, a second MOS transistor, a third MOS transistor, and a fourth MOS transistor. Both the first and second MOS transistors are each coupled between the voltage reference terminal and the first data interface. Both the third and fourth MOS transistors are each coupled between the ground potential reference terminal and the second data interface. All four transistors are configured as diodes.